The present invention relates to fasteners and more particularly to laminated nuts.
Laminated nuts are used as an alternative to conventional “solid” nuts in a variety of applications. Rather than a conventional solid body, laminated nuts include a number of stacked, coned disc springs that are retained together by an outer cage. The cage and disc springs collectively occupy essentially the same volume as a counterpart conventional solid nut. The interior of the disc springs are tapped so that the assembly can be threaded onto a bolt or other threaded shaft in a generally conventional manner. The cage and disc springs can be hex shaped so that the laminated nut can be installed and removed using the same tools used with conventional solid hex nuts. Examples of laminated nut structures are shown and described in U.S. Pat. No. 4,383,787, issued to Reynolds on May 17, 1983.
Unlike solid nuts, laminated nuts deform under load to grip the bolt and provide supplemental retention not provided by conventional solid nuts. In this regard, the individual disc springs have a relatively shallow cone shape and are manufactured from an elastic, resilient material. In use, conventional laminated nuts travel freely on the bolt until initial seating. Once seated, additional torque and rotation compresses and partially flattens the conical disc springs, whereby a mechanical interference occurs between the thread flanks of the nut and bolt; it is believed that this is at least partially due to a change in hole size of the nut as the conical discs flatten. The resultant thread interference and retained spring load between thread flanks resists unloading that might otherwise occur as a result of tensile or vibrational loads. Thus, the independently loaded conical spring threaded segments when flattened create a thread interference that tends to lock the nut against rotation or loosening when subject to loads.
As can be seen, the final tightening stage, which causes disc deformation, provides a locking action that helps to secure the laminated nut on the bolt. It is therefore typically desirable to ensure that the laminated nut has been sufficiently tightened to provide the desired amount of deformation and supplemental retention. It is also typically desirable to ensure that a tightened laminated nut does not back off over time and therefore lose the supplemental retention benefits associated with disc deformation.